Since the expression levels of the TGF-β pathway and BAMBI in lung tissue, alveolar macrophages and CD4+ T cells in peripheral blood from COPD patients have been studied [24, 25, 28], here, we examined the relative expression of the TGF-β pathway and BAMBI in monocyte-derived macrophages in COPD.As shown in Fig. 3a, b and c, we observed a decreased expression of TGF-β1, TGF-βRI/II and p-SMAD2/3 and an increased expression of BAMBI in the severe and very severe groups (n = 6) compared with the HC and HS groups. Here, CD4 is linked to chronic obstructive pulmonary disease.